diff --git a/CMakeLists.txt b/CMakeLists.txt
index 627e5ad..f7f6a7c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -59,9 +59,5 @@ install(FILES include/serial/serial.h include/serial/v8stdint.h
 
 ## Tests
 if(CATKIN_ENABLE_TESTING)
-    catkin_add_gtest(${PROJECT_NAME}-test tests/serial_tests.cc)
-    target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME} ${Boost_LIBRARIES})
-    if(UNIX AND NOT APPLE)
-        target_link_libraries(${PROJECT_NAME}-test util)
-    endif()
+    add_subdirectory(tests)
 endif()
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
new file mode 100644
index 0000000..38718e6
--- /dev/null
+++ b/tests/CMakeLists.txt
@@ -0,0 +1,10 @@
+if(UNIX)
+    catkin_add_gtest(${PROJECT_NAME}-test unix_serial_tests.cc)
+    target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME} ${Boost_LIBRARIES})
+    if(NOT APPLE)
+        target_link_libraries(${PROJECT_NAME}-test util)
+    endif()
+
+    catkin_add_gtest(${PROJECT_NAME}-test-timer unit/unix_timer_tests.cc)
+    target_link_libraries(${PROJECT_NAME}-test-timer ${PROJECT_NAME})
+endif()
diff --git a/tests/unit/unix_timer_tests.cc b/tests/unit/unix_timer_tests.cc
new file mode 100644
index 0000000..5bbd1ed
--- /dev/null
+++ b/tests/unit/unix_timer_tests.cc
@@ -0,0 +1,63 @@
+#include "gtest/gtest.h"
+#include "serial/impl/unix.h"
+
+#include <unistd.h>
+#include <stdlib.h>
+
+using serial::MillisecondTimer;
+
+namespace {
+
+/**
+ * Do 100 trials of timing gaps between 0 and 19 milliseconds.
+ * Expect accuracy within one millisecond.
+ */
+TEST(timer_tests, short_intervals) {
+  for (int trial = 0; trial < 100; trial++)
+  {
+    uint32_t ms = rand() % 20;
+    MillisecondTimer mt(ms);
+    usleep(1000 * ms);
+    int32_t r = mt.remaining(); 
+
+    // 1ms slush, for the cost of calling usleep.
+    EXPECT_NEAR(r+1, 0, 1);
+  }
+}
+
+TEST(timer_tests, overlapping_long_intervals) {
+  MillisecondTimer* timers[10];
+
+  // Experimentally determined. Corresponds to the extra time taken by the loops,
+  // the big usleep, and the test infrastructure itself.
+  const int slush_factor = 14;
+
+  // Set up the timers to each time one second, 1ms apart.
+  for (int t = 0; t < 10; t++)
+  {
+    timers[t] = new MillisecondTimer(1000);
+    usleep(1000);
+  }
+
+  // Check in on them after 500ms.
+  usleep(500000);
+  for (int t = 0; t < 10; t++)
+  {
+    EXPECT_NEAR(timers[t]->remaining(), 500 - slush_factor + t, 5);
+  }
+
+  // Check in on them again after another 500ms and free them.
+  usleep(500000);
+  for (int t = 0; t < 10; t++)
+  {
+    EXPECT_NEAR(timers[t]->remaining(), -slush_factor + t, 5);
+    delete timers[t];
+  }
+}
+
+}  // namespace
+
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
diff --git a/tests/serial_tests.cc b/tests/unix_serial_tests.cc
similarity index 100%
rename from tests/serial_tests.cc
rename to tests/unix_serial_tests.cc